Liquid crystal display and method of driving liquid crystal display

ABSTRACT

A liquid crystal display includes scanning lines and signal lines arranged in a matrix pattern on a TFT substrate, a pixel being formed at a crossing portion of each scanning line and each signal line, and including a TFT that is connected to each scanning line and each signal line, first nonlinear resistance elements formed respectively in the scanning lines, each of which being connected to one scanning line at one end thereof and to a short ring power-supply line for a scanning line at another end thereof, and second nonlinear resistance elements formed respectively in the signal lines, each of which being connected to one signal line at one end thereof and to a short ring power-supply line for a signal line at another end thereof. A voltage is applied to the first and second nonlinear resistance elements independently of each scanning line and each signal line.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a liquid crystal display (LCD) of anactive matrix type in which thin film transistors (TFTs) are used asswitching devices, and to a method of driving the liquid crystaldisplay.

Description of the Background Art

A TFT substrate including TFTs as switching devices is utilized in, forexample, an electro-optical device such as a liquid crystal displaybeing a display device that utilizes liquid crystals and alight-emitting display device being a display device that utilizes lightemitting diodes (LEDs). A semiconductor device such as a TFT has afeature in low power consumption and its thin profile, and is activelyapplied to a flat panel display.

In the liquid crystal display, there are a simple matrix LCD and aTFT-LCD that uses TFTs as switching devices. The TFT-LCD is superior tothe simple matrix LCD in display quality, and is widely used in displayproducts such as a mobile computer, a notebook computer, and atelevision.

In general, the TFT-LCD has a structure in which a liquid crystal layeris sandwiched between a TFT substrate including a plurality of TFTs thatare arranged in arrays and an opposing substrate including a colorfilter or the like. A polarizing plate is provided in each of asubstrate on a front surface side of the liquid crystal display and asubstrate on a back surface side thereof, and a backlight is provided ona further outer side of the back surface side. With such a structure,the TFT-LCD can perform satisfactory color display.

As a driving mode for the liquid crystals in the liquid crystal display,there are a vertical electric-field mode such as a twisted nematic (TN)mode and a vertical alignment (VA) mode, and a horizontal electric-fieldmode such as an in-plane switching mode and a fringe field switching(FFS) mode. In general, the liquid crystal display of a horizontalelectric-field mode is more advantageous than the liquid crystal displayof a vertical electric-field mode in realizing a wide viewing angle, andis becoming the mainstream in display products such as a personalcomputer and an on-vehicle display device.

In the liquid crystal display of a vertical electric-field mode astypified by the TN mode, a pixel electrode to be applied with a voltagein accordance with an image signal is arranged in the TFT substrate, anda common electrode to be applied with a common voltage being a fixedvoltage is arranged in the opposing substrate. The liquid crystals ofthe liquid crystal layer are driven by an electric field in asubstantially vertical direction with respect to a display surface ofthe liquid crystal display.

On the other hand, in the liquid crystal display of a horizontalelectric-field mode, both of the pixel electrode and the commonelectrode are arranged in the TFT substrate. The liquid crystals of theliquid crystal layer are driven by an electric field in a substantiallyhorizontal direction with respect to the display surface of the liquidcrystal display. Particularly, in the TFT substrate of the liquidcrystal display adopting the FFS mode, the pixel electrode and thecommon electrode are arranged to be opposed vertically throughintermediation of an insulating film. In this case, any one of the pixelelectrode and the common electrode may be arranged on the back surfaceside. The electrode arranged on the back surface side is formed into aflat-plate-like shape, and the electrode arranged on the front surfaceside, that is, on a side close to the liquid crystal layer, is formedinto a lattice shape or a comb-tooth-like shape having slits.

On the TFT substrate, scanning lines and signal lines are arranged in amatrix pattern, and a pixel is formed at a crossing portion of thescanning line and the signal line in a display region. The pixel isformed of the TFT, a storage capacitor, the pixel electrode, and thecommon electrode. In a frame region outside the display region, ascanning-line driving circuit for driving the scanning lines and asignal-line driving circuit for driving the signal lines are arranged. Asignal processing circuit is arranged outside the TFT substrate throughintermediation of flexible printed circuits (FPCs) or the like. Thescanning-line driving circuit and the signal-line driving circuit may beframed as a separate integrated circuit (IC) from the TFT substrate, andmay be formed in the TFT substrate in the same manufacturing process asa manufacturing process for forming the TFTs.

When display is performed in the TFT-LCD, the scanning-line drivingcircuit and the signal-line driving circuit apply a voltage to eachscanning line and each signal line in accordance with a signal inputfrom the signal processing circuit. Then, the TFT that forms the pixelis driven and an electric charge is injected into the pixel electrode tothereby apply a voltage to the liquid crystals, and thus predetermineddisplay is performed. At this time, the scanning-line driving circuitturns the scanning lines into an on state by applying a voltagesequentially from one scanning line to another only during apredetermined time period, that is, turns the TFTs into an on state, andduring a time period other than the above turns the scanning lines intoan off state in which a voltage is not applied, that is, turns the TFTsinto an off state. The signal-line driving circuit applies a voltage tothe signal lines that cross with the scanning lines in accordance with adisplay gradation.

When the scanning-line driving circuit and the signal-line drivingcircuit abruptly suspend the application of the voltage to the scanninglines and the signal lines at the time of suspending the display of theTFT-LCD, the electric charge injected into the pixel electrode mayremain to be retained therein, which may generate a phenomenon called“image retention” in which a particular display continues to remain. Theimage retention is an unpreferable state for the display of the TFT-LCD.

As a countermeasure for the above, hitherto, there is disclosed atechnology in which a GND voltage, that is, a voltage of 0 V, is appliedto the signal lines and the common electrode after all of the scanninglines are turned into an on state, and then all the electrical powersupplied to the TFT-LCD is turned off so that the electric charge doesnot remain in the pixel electrode at the time of suspending the display(refer to Japanese Patent Application Laid-Open No. 2001-22326, forexample). Note that, a GND voltage is hereinafter also referred to as aground voltage.

Further, there is disclosed a technology in which a nonlinear resistanceelement is connected to each of the scanning lines and the signal lines,to thereby discharge the electric charge retained in the scanning linesand the signal lines through the nonlinear resistance element (refer toJapanese Patent Application Laid-Open No. 10-10494, for example).

In Japanese Patent Application Laid-Open No. 2001-22326, the IC fordriving the scanning lines needs to have a function of turning all ofthe scanning lines into an on state, and hence there is a problem inrequiring a cost. Further, in a case where the circuit for driving thescanning lines is formed in the TFT substrate in the same manufacturingprocess as the manufacturing process for forming the TFTs, there is aproblem in difficulty of assigning the function of turning all of thescanning lines into an on state to the circuit.

In Japanese Patent Application Laid-Open No. 10-10494, an electriccharge cannot be prevented from remaining in the pixel electrode at thetime of suspending the display, and hence there is a problem ingenerating image retention.

SUMMARY

The present invention has an object to provide a liquid crystal displaycapable of preventing image retention from being generated with simpleconfiguration at the time of suspending display, and a method of drivinga liquid crystal display.

In order to solve the above-mentioned problems, a liquid crystal displayaccording to the present invention includes a plurality of scanninglines and a plurality of signal lines, a pixel, a plurality of firstnonlinear resistance elements, and a plurality of second nonlinearresistance elements. The plurality of scanning lines and the pluralityof signal lines are arranged in a matrix pattern on a substrate. Thepixel is formed at a crossing portion of each of the plurality ofscanning lines and each of the plurality of signal lines, and includes athin film transistor that is connected to each of the plurality ofscanning lines and each of the plurality of signal lines. The pluralityof first nonlinear resistance elements are formed respectively in theplurality of scanning lines. Each of the plurality of first nonlinearresistance elements is connected to one of the plurality of scanninglines at one end thereof and is connected to a first short ring line atanother end thereof. The plurality of second nonlinear resistanceelements are formed respectively in the plurality of signal lines. Eachof the plurality of second nonlinear resistance elements is connected toone of the plurality of signal lines at one end thereof and is connectedto a second short ring line at another end thereof. A voltage is appliedto the plurality of first nonlinear resistance elements and theplurality of second nonlinear resistance elements independently of eachof the plurality of scanning lines and each of the plurality of signallines.

According to the present invention, the liquid crystal display includesthe plurality of scanning lines and the plurality of signal lines, thepixel, the plurality of first nonlinear resistance elements, and theplurality of second nonlinear resistance elements. The plurality ofscanning lines and the plurality of signal lines are arranged in amatrix pattern on the substrate. The pixel is formed at the crossingportion of each of the plurality of scanning lines and each of theplurality of signal lines, and includes the thin film transistor that isconnected to each of the plurality of scanning lines and each of theplurality of signal lines. The plurality of first nonlinear resistanceelements are formed respectively in the plurality of scanning lines.Each of the plurality of first nonlinear resistance elements isconnected to one of the plurality of scanning lines at one end thereofand is connected to the first short ring line at another end thereof.The plurality of second nonlinear resistance elements are formedrespectively in the plurality of signal lines. Each of the plurality ofsecond nonlinear resistance elements is connected to one of theplurality of signal lines at one end thereof and is connected to thesecond short ring line at another end thereof. A voltage is applied tothe plurality of first nonlinear resistance elements and the pluralityof second nonlinear resistance elements independently of each of theplurality of scanning lines and each of the plurality of signal lines.Hence, it is possible to prevent image retention from being generatedwith simple configuration at the time of suspending display.

Further, a liquid crystal display according to the present inventionincludes a plurality of scanning lines and a plurality of signal lines,a pixel, a short ring line, inspection thin film transistors on ascanning line side, an inspection scanning line, inspection thin filmtransistors on a signal line side, and an inspection signal line. Theplurality of scanning lines and the plurality of signal lines arearranged in a matrix pattern on a substrate. The pixel is formed at acrossing portion of each of the plurality of scanning lines and each ofthe plurality of signal lines, and includes a thin film transistor thatis connected to each of the plurality of scanning lines and each of theplurality of signal lines. The short ring line is connected to each ofthe plurality of scanning lines and each of the plurality of signallines. The inspection thin film transistors on a scanning line side areformed respectively in the plurality of scanning lines. The inspectionscanning line is arranged so as to be connected to each of the pluralityof scanning lines through intermediation of each of the inspection thinfilm transistors on a scanning line side. The inspection thin filmtransistors on a signal line side are formed respectively in theplurality of signal lines. The inspection signal line is arranged so asto be connected to each of the plurality of signal lines throughintermediation of each of the inspection thin film transistors on asignal line side.

Further, the liquid crystal display includes the plurality of scanninglines and the plurality of signal lines, the pixel, the short ring line,the inspection thin film transistors on a scanning line side, theinspection scanning line, the inspection thin film transistors on asignal line side, and the inspection signal line. The plurality ofscanning lines and the plurality of signal lines are arranged in amatrix pattern on the substrate. The pixel is formed at the crossingportion of each of the plurality of scanning lines and each of theplurality of signal lines, and includes the thin film transistor that isconnected to each of the plurality of scanning lines and each of theplurality of signal lines. The short ring line is connected to each ofthe plurality of scanning lines and each of the plurality of signallines. The inspection thin film transistors on a scanning line side areformed respectively in the plurality of scanning lines. The inspectionscanning line is arranged so as to be connected to each of the pluralityof scanning lines through intermediation of each of the inspection thinfilm transistors on a scanning line side. The inspection thin filmtransistors on a signal line side are formed respectively in theplurality of signal lines. The inspection signal line is arranged so asto be connected to each of the plurality of signal lines throughintermediation of each of the inspection thin film transistors on asignal line side. Hence, it is possible to prevent image retention frombeing generated with simple configuration at the time of suspendingdisplay.

Further, the present invention is intended for a method of driving aliquid crystal display, which is a method of driving a liquid crystaldisplay at the time of suspending display. The method of driving aliquid crystal display according to the present invention includes thefollowing steps (a) to (e). The step (a) is to suspend application of avoltage to each of the plurality of scanning lines. The step (b) is toapply, after the step (a), a predetermined voltage to each of theplurality of scanning lines via the first short ring line and each ofthe plurality of first nonlinear resistance elements. The step (c) is toapply, after the step (a), a ground voltage to each of the plurality ofsignal lines via the second short ring line and each of the plurality ofsecond nonlinear resistance elements. The step (d) is to apply, afterthe step (a), a ground voltage to a common electrode that forms thepixel. The step (e) is to suspend, after the step (b), the step (c), andthe step (d), the application of the voltage to each of the plurality ofscanning lines, each of the plurality of signal lines, and the commonelectrode in the step (b), the step (c), and the step (d).

Further, the method of driving a liquid crystal display is a method ofdriving a liquid crystal display at the time of suspending display. Themethod of driving a liquid crystal display includes the following steps(a) to (e). The step (a) is to suspend the application of the voltage toeach of the plurality of scanning lines. The step (b) is to apply, afterthe step (a), the predetermined voltage to each of the plurality ofscanning lines via the first short ring line and each of the pluralityof first nonlinear resistance elements. The step (c) is to apply, afterthe step (a), the ground voltage to each of the plurality of signallines via the second short ring line and each of the plurality of secondnonlinear resistance elements. The step (d) is to apply, after the step(a), the ground voltage to the common electrode that forms the pixel.The step (e) is to suspend, after the step (b), the step (c), and thestep (d), the application of the voltage to each of the plurality ofscanning lines, each of the plurality of signal lines, and the commonelectrode in the step (b), the step (c), and the step (d). Hence, it ispossible to prevent image retention from being generated with simpleconfiguration at the time of suspending display.

Further, the present invention is intended for a method of driving aliquid crystal display, which is a method of driving a liquid crystaldisplay at the time of suspending display. The method of driving aliquid crystal display according to the present invention includes thefollowing steps (a) to (e). The step (a) is to suspend application of avoltage to each of the plurality of scanning lines and each of theplurality of signal lines. The step (b) is to apply, after the step (a),a predetermined voltage to each of the plurality of scanning lines viathe inspection scanning line and the inspection thin film transistors ona scanning line side. The step (c) is to apply, after the step (a), aground voltage to each of the plurality of signal lines via theinspection signal line and the inspection thin film transistors on asignal line side. The step (d) is to apply, after the step (a), a groundvoltage to a common electrode that forms the pixel. The step (e) is tosuspend, after the step (b), the step (c), and the step (d), theapplication of the voltage to each of the plurality of scanning lines,each of the plurality of signal lines, and the common electrode in thestep (b), the step (c), and the step (d).

Further, the method of driving a liquid crystal display is a method ofdriving a liquid crystal display at the time of suspending display. Themethod of driving a liquid crystal display includes the following steps(a) to (e). The step (a) is to suspend the application of the voltage toeach of the plurality of scanning lines and each of the plurality ofsignal lines. The step (b) is to apply, after the step (a), thepredetermined voltage to each of the plurality of scanning lines via theinspection scanning line and the inspection thin film transistors on ascanning line side. The step (c) is to apply, after the step (a), theground voltage to each of the plurality of signal lines via theinspection signal line and the inspection thin film transistors on asignal line side. The step (d) is to apply, after the step (a), theground voltage to the common electrode that forms the pixel. The step(e) is to suspend, after the step (b), the step (c), and the step (d),the application of the voltage to each of the plurality of scanninglines, each of the plurality of signal lines, and the common electrodein the step (b), the step (c), and the step (d). Hence, it is possibleto prevent image retention from being generated with simpleconfiguration at the time of suspending display.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for illustrating an example of a configuration of aliquid crystal display according to a first preferred embodiment of thepresent invention.

FIG. 2 is a view for illustrating an equivalent circuit of nonlinearresistance elements according to the first preferred embodiment of thepresent invention.

FIG. 3 is a view for illustrating an example of a configuration of theliquid crystal display according to a second preferred embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described below inaccordance with the drawings.

First Preferred Embodiment

<Configuration>

FIG. 1 is a view for illustrating an example of a configuration of aliquid crystal display according to a first preferred embodiment of thepresent invention, which illustrates a circuit configuration foractivating liquid crystals 14. Note that, a color filter substrate and apolarizing plate that form the liquid crystal display are unrelated tothe circuit for activating the liquid crystals, and hence illustrationthereof is omitted in FIG. 1. Further, a backlight is operatedindependently from a TFT substrate 1, and hence illustration thereof isomitted.

The liquid crystal display includes the TFT substrate 1 and a controlcircuit board 2, and the TFT substrate 1 is connected to the controlcircuit board 2 through intermediation of FPCs 3. In the TFT substrate1, a scanning-line driving circuit 4 and a signal-line driving circuit 5are provided. The scanning-line driving circuit 4 is connected to thecontrol circuit board 2 through intermediation of an image power-supplyline 6 for a scanning line and the FPCs 3. The signal-line drivingcircuit 5 is connected to the control circuit board 2 throughintermediation of an image power-supply line 7 for a signal line and theFPCs 3. An image signal, electrical power, and the like are supplied tothe control circuit board 2 from the outside. Note that, each of theimage power-supply line 6 for a scanning line and the image power-supplyline 7 for a signal line is Ruined of a plurality of lines, but iscollectively illustrated as one line in the example of FIG. 1.

A plurality of scanning lines 8 and a plurality of signal lines 9 arearranged in a matrix pattern on the TFT substrate 1, and a pixel 16 isformed at a crossing portion of the scanning line 8 and the signal line9 in a display region 10. The pixel 16 is formed of a TFT 11 connectedto the scanning line 8 and the signal line 9, a pixel electrode 12, acommon electrode 13, the liquid crystals 14, and a storage capacitor 15.

A nonlinear resistance element 19 being a first nonlinear resistanceelement is formed in each of the scanning lines 8. The nonlinearresistance element 19 is connected to the scanning line 8 at one endthereof, and is connected to a short ring power-supply line 17 for ascanning line being a first short ring line at another end thereof. Theshort ring power-supply line 17 for a scanning line is connected to thecontrol circuit board 2 through intermediation of the FPCs 3. Anonlinear resistance element 20 being a second nonlinear resistanceelement is formed in each of the signal lines 9. The nonlinearresistance element 20 is connected to the signal line 9 at one endthereof, and is connected to a short ring power-supply line 18 for asignal line being a second short ring line at another end thereof. Theshort ring power-supply line 18 for a signal line is connected to thecontrol circuit board 2 through intermediation of the FPCs 3. A voltageis applied to the nonlinear resistance elements 19 and 20 from thecontrol circuit board 2. That is, a voltage is applied to the nonlinearresistance elements 19 and 20 independently of the scanning lines 8 andthe signal lines 9.

<Operation>

First, description is given to a case where arbitrary display isperformed on the liquid crystal display.

The display is realized by applying a voltage to the liquid crystals 14of the pixel 16 formed in a matrix pattern in the display region 10.Specifically, the control circuit board 2 supplies an image signal and apower-supply voltage to each of the scanning-line driving circuit 4 andthe signal-line driving circuit 5 via the image power-supply line 6 fora scanning line and the image power-supply line 7 for a signal line.Further, the control circuit board 2 applies a common voltage being afixed voltage to the short ring power-supply line 17 for a scanning lineand the short ring power-supply line 18 for a signal line.

The scanning-line driving circuit 4 applies a voltage to turn thescanning lines 8 into an on state sequentially from one line to another.Further, the signal-line driving circuit 5 applies a voltage to thesignal lines 9 so that an arbitrary pixel 16 performs predetermineddisplay in accordance with the application of the voltage from thescanning-line driving circuit 4 to the scanning lines 8. That is, whenan electric charge is injected into the pixel electrode 12 from thesignal lines 9 at the time of an on state of the TFT 11 of each pixel16, transmittance of the liquid crystals 14 changes in accordance with avoltage generated between the pixel electrode 12 and the commonelectrode 13. At this time, a light from a backlight is transmitted tothe liquid crystals 14, and thus a desired image is displayed. Notethat, for example, a voltage of 24 V is applied to the scanning lines 8to turn the scanning lines 8 into an on state, and a voltage of −6 V isapplied to the scanning lines 8 to turn the scanning lines 8 into an offstate. Further, a voltage of from 11 V to 0 V is applied to the signallines 9 and the pixel electrode 12, and a voltage of 5 V is applied tothe common electrode 13.

Next, description is given to a case where the display in the liquidcrystal display is turned off, that is, the display is suspended.

Suspension of the display is realized by suspending the supply of theimage signal and the power-supply voltage from the control circuit board2 to each of the scanning-line driving circuit 4 and the signal-linedriving circuit 5. At this time, in a case where resistance of the TFT11, the liquid crystals 14, and the storage capacitor 15 in the pixel 16is high, there is a problem in that the liquid crystals 14 remain to beapplied with a voltage due to a long period of maintenance of theelectric charge retained in the pixel electrode 12 and the display stateis maintained due to the transmittance of the liquid crystals 14,resulting in an appearance of image retention. In order to solve such aproblem, the control circuit board 2 suspends the operation of thescanning-line driving circuit 4 to suspend the application of thevoltage from the scanning-line driving circuit 4 to the scanning lines 8at the time of suspending the display of the liquid crystal display.After that, the control circuit board 2 applies a voltage to thescanning lines 8 via the short ring power-supply line 17 for a scanningline and the nonlinear resistance element 19. Further, the controlcircuit board 2 applies a ground voltage to the signal lines 9 via theshort ring power-supply line 18 for a signal line and the nonlinearresistance element 20. Further, a ground voltage is applied to thecommon electrode 13. With this, the signal lines 9 and the commonelectrode 13 have substantially the same potential, and the electriccharge retained in the pixel electrode 12 is removed. Note that, thevoltage to be applied to the scanning lines 8 via the short ringpower-supply line 17 for a scanning line and the nonlinear resistanceelement 19 only needs to be a voltage to turn the scanning lines 8 intoan on state, that is, a voltage to turn the TFT 11 communicating to thescanning lines 8 into an on state, and a range of approximately from 5 Vto 40 V suffices, for example. Accordingly, the voltage to be applied tothe scanning lines 8 via the short ring power-supply line 17 for ascanning line and the nonlinear resistance element 19 need not be thesame as the voltage applied from the scanning-line driving circuit 4 tothe scanning lines 8 at the time when the liquid crystal displayperforms display.

After that, the application of the voltage to the scanning lines 8 viathe short ring power-supply line 17 for a scanning line and thenonlinear resistance element 19, the application of the ground voltageto the signal lines 9 via the short ring power-supply line 18 for asignal line and the nonlinear resistance element 20, and the applicationof the ground voltage to the common electrode 13 are suspended.

As a time period from the application of the voltage via the nonlinearresistance element until the suspension, a time period during which atleast one line of the scanning lines 8 is in an on state or longer isnecessary. For example, in a case where one thousand scanning lines 8are provided and the display is rewritten with a period of 60 Hz, alower limit of the time period is 16.7 microseconds, and at least 5microseconds or longer are necessary. An upper limit for the time periodis not provided in particular. However, it is not preferable to takeexcessive time for the suspension of the display of the liquid crystaldisplay, and hence approximately several seconds suffice at the longest.

The nonlinear resistance elements 19 and 20 may be bidirectional diodesformed in the same manufacturing process as the TFT 11 provided in thepixel 16. FIG. 2 is a view for illustrating an equivalent circuit of thenonlinear resistance elements 19 and 20 being bidirectional diodes. Asillustrated in FIG. 2, the bidirectional diode is formed by connecting aforward diode and a reverse diode in parallel. That is, the nonlinearresistance elements 19 and 20 are each formed of a plurality of TFTs. Inthe bidirectional diode, a current does not flow when a voltage betweenterminals 21 and 22 is small, but a current flows when the voltagebetween the terminals 21 and 22 is large, and hence the bidirectionaldiode is operated so that difference of the voltage between theterminals 21 and 22 always approaches to zero. Accordingly, as describedabove, when a voltage is applied to the scanning lines 8 via the shortring power-supply line 17 for a scanning line and the nonlinearresistance element 19 after suspending the application of the voltagefrom the scanning-line driving circuit 4 to the scanning lines 8, thescanning lines 8 can be turned into an on state. After that, when theapplication of the voltage to the scanning lines 8 via the short ringpower-supply line 17 for a scanning line and the nonlinear resistanceelement 19, the application of the ground voltage to the signal lines 9via the short ring power-supply line 18 for a signal line and thenonlinear resistance element 20, and the application of the groundvoltage to the common electrode 13 are suspended, a current flows fromthe scanning lines 8 via the nonlinear resistance element 19, therebybeing capable of reducing the voltage of the scanning lines 8.

In this manner, the nonlinear resistance elements 19 and 20 and the TFT11 of the pixel 16 can be formed in the same manufacturing process, andhence the above-mentioned function can be obtained at a low cost. Notethat, in the example of FIG. 2, the nonlinear resistance elements 19 and20 are each formed of two TFTs. However, the nonlinear resistanceelements 19 and 20 are not limited thereto, and may be formed of moreTFTs. Arranging TFTs in series raises resistance and arranging TFTs inparallel lowers resistance, and hence it is possible to adjustresistance values of the nonlinear resistance elements 19 and 20.Further, the short ring line can also be formed in the samemanufacturing process as the TFT 11, thus attaining effects ofpreventing destruction of elements due to static electricity that may begenerated during the manufacturing process.

In a case where the scanning-line driving circuit 4 is an IC attached tothe TFT substrate 1 from the outside, that is, in a case where thescanning-line driving circuit 4 is provided separately from the TFTsubstrate 1, it is possible to apply the scanning-line driving circuit 4that lacks the function of simultaneously turning all of the scanninglines 8 into an on state. Accordingly, the number of functions of thescanning-line driving circuit 4 can be reduced, and hence it is possibleto apply the low-cost scanning-line driving circuit 4.

Further, in a case where the scanning-line driving circuit 4 is formedin the same manufacturing process as the TFT 11 of the pixel 16, thatis, in a case where the scanning-line driving circuit 4 is provided onthe TFT substrate 1, the scanning-line driving circuit 4 only needs tohave a function of turning the scanning lines 8 sequentially into an onstate, and hence it is possible to form the scanning-line drivingcircuit 4 with simple configuration.

Next, description is given to a method of applying a ground voltage tothe signal lines 9 at the time of suspending the display of the liquidcrystal display.

When the display of the liquid crystal display is suspended, the controlcircuit board 2 suspends the operation of the signal-line drivingcircuit 5 to suspend the application of the voltage from the signal-linedriving circuit 5 to the signal lines 9. After that, the control circuitboard 2 may apply a ground voltage to the short ring power-supply line18 for a signal line.

In a case where the signal-line driving circuit 5 is an IC attached tothe TFT substrate 1 from the outside, that is, in a case where thesignal-line driving circuit 5 is provided separately from the TFTsubstrate 1, similarly to the scanning-line driving circuit 4, it ispossible to apply the low-cost signal-line driving circuit 5 with asmall number of functions.

Further, in a case where the signal-line driving circuit 5 is formed inthe same manufacturing process as the TFT 11 of the pixel 16, that is,in a case where the signal-line driving circuit 5 is provided on the TFTsubstrate 1, it is possible to form the signal-line driving circuit 5with simple configuration. Note that, if the scanning-line drivingcircuit 4 has a function of outputting a ground voltage, such a functionmay be used.

Next, description is given to TFTs to be foil led in the TFT substrate1.

As described above, as the TFTs to be formed in the TFT substrate 1, theTFT 11 of the pixel 16 and the TFTs that form the nonlinear resistanceelements 19 and 20 may be employed, for example. As an active layerbeing a channel layer of those TFTs, a material having Si as a maincomponent thereof may be used, such as amorphous silicon (a-Si) orcrystalline silicon (p-Si). Such a material has a comparatively largeleakage current of the TFTs and hence image retention is less liable tobe generated, but such a case is considered that a threshold voltage ofthe TFTs is shifted to be positive, for example. In this case, imageretention is liable to be generated at the time of suspending thedisplay of the liquid crystal display, but the generation of the imageretention can be easily prevented by adopting the configuration of theliquid crystal display according to this first preferred embodimentdescribed above.

Further, as another example, an oxide semiconductor formed of a zincoxide (ZnO)-based material or an amorphous InGaZnO-based material thatis obtained by adding gallium oxide (Ga₂O₃) and indium oxide (In₂O₃) tozinc oxide may be used for the active layer of the TFTs. The oxidesemiconductor has a smaller leakage current of the TFTs than amorphoussilicon and crystalline silicon and hence image retention is more liableto be generated, but the generation of the image retention can be easilyprevented by adopting the configuration of the liquid crystal displayaccording to this first preferred embodiment described above.

From the above, according to this first preferred embodiment, it ispossible to prevent image retention from being generated with simpleconfiguration at the time of suspending the display. Accordingly, theliquid crystal display having excellent display property can beobtained.

Note that, the above-mentioned description is merely an example, and adriving mode for the liquid crystals in the liquid crystal display maybe any driving mode, such as a TN mode, an in-plane switching mode, andan FFS mode. Particularly, the present invention is effective in thecase of such a driving mode that the resistance of the liquid crystalsbecomes high. The liquid crystal display may be a liquid crystal displayof a reflection type that does not include a backlight. A part of thefunctions of the control circuit board 2 may be included in thescanning-line driving circuit 4 and the signal-line driving circuit 5.

Second Preferred Embodiment

<Configuration>

FIG. 3 is a view for illustrating an example of a configuration of theliquid crystal display according to a second preferred embodiment of thepresent invention, which illustrates a circuit configuration foractivating the liquid crystals 14. As illustrated in FIG. 3, the liquidcrystal display according to this second preferred embodiment has afeature in including a short ring power-supply line 23, an inspectionterminal 24, an inspection TFT switching line 25 on a scanning lineside, an inspection TFT 26 on a scanning line side, an inspectionscanning line 27, an inspection TFT switching line 28 on a signal lineside, an inspection TFT 29 on a signal line side, and an inspectionsignal line 30. Other configurations and operations are similar to thoseof the first preferred embodiment, and hence detailed descriptionthereof is herein omitted.

The short ring power-supply line 23 being a short ring line is connectedto each of the scanning lines 8 and each of the signal lines 9 throughintermediation of the nonlinear resistance element. The inspection TFT26 on a scanning line side being an inspection thin film transistor on ascanning line side is formed in each of the plurality of scanning lines.The inspection scanning line 27 is arranged so as to be connected toeach of the scanning lines 8 through intermediation of the inspectionTFT 26 on a scanning line side. The inspection TFT 29 on a signal lineside being an inspection thin film transistor on a signal line side isformed in each of the plurality of signal lines. The inspection signalline 30 is arranged so as to be connected to each of the signal lines 9through intermediation of the inspection TFT 29 on a signal line side.

The nonlinear resistance element 19 being the first nonlinear resistanceelement is formed in each of the scanning lines 8. The nonlinearresistance element 19 is connected to the scanning line 8 at one endthereof, and is connected to the short ring power-supply line 23 atanother end thereof. The nonlinear resistance element 20 being thesecond nonlinear resistance element is formed in each of the signallines 9. The nonlinear resistance element 20 is connected to the signalline 9 at one end thereof, and is connected to the short ringpower-supply line 23 at another end thereof. Note that, the nonlinearresistance elements 19 and 20 may be omitted.

<Operation>

In the following, description is given to an operation at the time ofperforming a simplified inspection and an operation at the time ofsuspending the display of the liquid crystal display.

<Operation at the Time of Performing Simplified Inspection>

The simplified inspection inspects a state of the liquid crystal displayformed of the TFT substrate 1 and a color filter substrate (not shown)in the middle of the manufacturing under a state in which the TFTsubstrate 1 is out of connection with all of or any of the controlcircuit board 2, the FPCs 3, the scanning-line driving circuit 4, andthe signal-line driving circuit 5.

Specifically, a voltage is applied from the inspection terminal 24 tothe inspection TFT switching line 25 on a scanning line side to turn theinspection TFT 26 on a scanning line side into an on state. Then, avoltage is applied from the inspection terminal 24 to the scanning lines8 via the inspection scanning line 27. Further, a voltage is appliedfrom the inspection terminal 24 to the inspection TFT switching line 28on a signal line side to turn the inspection TFT 29 on a signal lineside into an on state. Then, a voltage is applied from the inspectionterminal 24 to the signal lines 9 via the inspection signal line 30.With this, whether or not the lines of the scanning lines 8 and thesignal lines 9 are disconnected can be determined, for example.

Note that, in FIG. 3, illustration of wiring of the common electrode 13is omitted. The inspection terminal 24, the inspection TFT switchingline 25 on a scanning line side, the inspection TFT 26 on a scanningline side, the inspection scanning line 27, the inspection TFT switchingline 28 on a signal line side, the inspection TFT 29 on a signal lineside, and the inspection signal line 30 can be formed in the samemanufacturing process as the TFT 11 of the pixel 16 and the like, andhence additional manufacturing processes for forming those componentsare not required. In FIG. 3, a configuration in which the scanning lines8 and the signal lines 9 are collectively operated is illustrated, but aconfiguration in which the scanning lines 8 and the signal lines 9 areoperated dividedly into a plurality of times may be employed.

<Operation at the Time of Suspending Display of Liquid Crystal Display>

In the following operation, in the configuration illustrated in FIG. 3,a premise is made on a state in which the control circuit board 2 andthe inspection terminal 24 are connected to allow an arbitrary voltageto be applied from the control circuit board 2 to the inspectionterminal 24.

When the display of the liquid crystal display is suspended, the controlcircuit board 2 suspends the operations of the scanning-line drivingcircuit 4 and the signal-line driving circuit 5. After that, the controlcircuit board 2 applies a voltage from the inspection terminal 24 to theinspection TFT switching line 25 on a scanning line side to turn theinspection TFT 26 on a scanning line side into an on state. Then, thecontrol circuit board 2 applies a voltage from the inspection terminal24 to the scanning lines 8 via the inspection scanning line 27, therebyturning all of the scanning lines 8 into an on state. Further, thecontrol circuit board 2 applies a voltage from the inspection terminal24 to the inspection TFT switching line 28 on a signal line side to turnthe inspection TFT 29 on a signal line side into an on state. Then, thecontrol circuit board 2 applies a ground voltage from the inspectionterminal 24 to the signal lines 9 via the inspection signal line 30. Atthis time, a ground voltage is also applied to the common electrode 13.After that, all of the voltages applied via the inspection terminal 24from the control circuit board 2 are suspended. With this, the electriccharge is eliminated in the pixel electrode 12, and thus image retentioncan be prevented from being generated.

From the above, according to this second preferred embodiment, it ispossible to prevent image retention from being generated with simpleconfiguration at the time of suspending the display. Accordingly, theliquid crystal display having excellent display property can beobtained.

Note that, in the present invention, each of the preferred embodimentsmay be freely combined and each of the preferred embodiments may bemodified or omitted as appropriate within the scope of the invention.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

What is claimed is:
 1. A liquid crystal display, comprising: a pluralityof scanning lines and a plurality of signal lines arranged in a matrixpattern on a substrate; a pixel being formed at a crossing portion ofeach of the plurality of scanning lines and each of the plurality ofsignal lines, and comprising a thin film transistor that is connected toeach of the plurality of scanning lines and each of the plurality ofsignal lines; a plurality of first nonlinear resistance elements formedrespectively in the plurality of scanning lines, each of the pluralityof first nonlinear resistance elements being connected to one of theplurality of scanning lines at one end thereof and being connected to afirst short ring line at another end thereof; and a plurality of secondnonlinear resistance elements formed respectively in the plurality ofsignal lines, each of the plurality of second nonlinear resistanceelements being connected to one of the plurality of signal lines at oneend thereof and being connected to a second short ring line at anotherend thereof, wherein a voltage is applied to the plurality of firstnonlinear resistance elements and the plurality of second nonlinearresistance elements independently of each of the plurality of scanninglines and each of the plurality of signal lines.
 2. The liquid crystaldisplay according to claim 1, wherein the plurality of first nonlinearresistance elements and the plurality of second nonlinear resistanceelements each comprise a plurality of thin film transistors.
 3. Theliquid crystal display according to claim 1, further comprising ascanning-line driving circuit for applying a voltage to each of theplurality of scanning lines, wherein the scanning-line driving circuitis provided separately from the substrate.
 4. The liquid crystal displayaccording to claim 1, further comprising a scanning-line driving circuitfor applying a voltage to each of the plurality of scanning lines,wherein the scanning-line driving circuit is provided on the substrate.5. The liquid crystal display according to claim 1, further comprising asignal-line driving circuit for applying a voltage to each of theplurality of signal lines, wherein the signal-line driving circuit isprovided separately from the substrate.
 6. The liquid crystal displayaccording to claim 1, further comprising a signal-line driving circuitfor applying a voltage to each of the plurality of signal lines, whereinthe signal-line driving circuit is provided on the substrate.
 7. Theliquid crystal display according to claim 1, wherein an active layer ofthe thin film transistor comprises Si as a main component thereof. 8.The liquid crystal display according to claim 1, wherein an active layerof the thin film transistor comprises an oxide semiconductor.
 9. Aliquid crystal display, comprising: a plurality of scanning lines and aplurality of signal lines arranged in a matrix pattern on a substrate; apixel being formed at a crossing portion of each of the plurality ofscanning lines and each of the plurality of signal lines, and comprisinga thin film transistor that is connected to each of the plurality ofscanning lines and each of the plurality of signal lines; a short ringline connected to each of the plurality of scanning lines and each ofthe plurality of signal lines; inspection thin film transistors on ascanning line side that are formed respectively in the plurality ofscanning lines; an inspection scanning line arranged so as to beconnected to each of the plurality of scanning lines throughintermediation of each of the inspection thin film transistors on ascanning line side; inspection thin film transistors on a signal lineside that are formed respectively in the plurality of signal lines; andan inspection signal line arranged so as to be connected to each of theplurality of signal lines through intermediation of each of theinspection thin film transistors on a signal line side.
 10. The liquidcrystal display according to claim 9, further comprising: a plurality offirst nonlinear resistance elements formed respectively in the pluralityof scanning lines, each of the plurality of first nonlinear resistanceelements being connected to one of the plurality of scanning lines atone end thereof and being connected to the short ring line at anotherend thereof; and a plurality of second nonlinear resistance elementsformed respectively in the plurality of signal lines, each of theplurality of second nonlinear resistance elements being connected to oneof the plurality of signal lines at one end thereof and being connectedto the short ring line at another end thereof.
 11. The liquid crystaldisplay according to claim 9, further comprising a scanning-line drivingcircuit for applying a voltage to each of the plurality of scanninglines, wherein the scanning-line driving circuit is provided separatelyfrom the substrate.
 12. The liquid crystal display according to claim 9,further comprising a scanning-line driving circuit for applying avoltage to each of the plurality of scanning lines, wherein thescanning-line driving circuit is provided on the substrate.
 13. Theliquid crystal display according to claim 9, further comprising asignal-line driving circuit for applying a voltage to each of theplurality of signal lines, wherein the signal-line driving circuit isprovided separately from the substrate.
 14. The liquid crystal displayaccording to claim 9, further comprising a signal-line driving circuitfor applying a voltage to each of the plurality of signal lines, whereinthe signal-line driving circuit is provided on the substrate.
 15. Theliquid crystal display according to claim 9, wherein an active layer ofthe thin film transistor comprises Si as a main component thereof. 16.The liquid crystal display according to claim 9, wherein an active layerof the thin film transistor comprises an oxide semiconductor. 170 Amethod of driving a liquid crystal display comprising the liquid crystaldisplay of claim 1, the method comprising the steps of: (a) suspendingapplication of a voltage to each of the plurality of scanning lines; (b)applying, after the step (a), a predetermined voltage to each of theplurality of scanning lines via the first short ring line and each ofthe plurality of first nonlinear resistance elements; (c) applying,after the step (a), a ground voltage to each of the plurality of signallines via the second short ring line and each of the plurality of secondnonlinear resistance elements; (d) applying, after the step (a), aground voltage to a common electrode that forms the pixel; and (e)suspending, after the step (b), the step (c), and the step (d), theapplication of the voltage to each of the plurality of scanning lines,each of the plurality of signal lines, and the common electrode in thestep (b), the step (c), and the step (d).
 18. The method of driving aliquid crystal display according to claim 17, wherein the predeterminedvoltage comprises a voltage to turn the plurality of scanning lines intoan on state and to turn the thin film transistor that is connected tothe plurality of scanning lines into an on state.
 19. A method ofdriving a liquid crystal display comprising the liquid crystal displayof claim 9, the method comprising the steps of: (a) suspendingapplication of a voltage to each of the plurality of scanning lines andeach of the plurality of signal lines; (b) applying, after the step (a),a predetermined voltage to each of the plurality of scanning lines viathe inspection scanning line and the inspection thin film transistors ona scanning line side; (c) applying, after the step (a), a ground voltageto each of the plurality of signal lines via the inspection signal lineand the inspection thin film transistors on a signal line side; (d)applying, after the step (a), a ground voltage to a common electrodethat forms the pixel; and (e) suspending, after the step (b), the step(c), and the step (d), the application of the voltage to each of theplurality of scanning lines, each of the plurality of signal lines, andthe common electrode in the step (b), the step (c), and the step (d).20. The method of driving a liquid crystal display according to claim19, wherein the predetermined voltage comprises a voltage to turn theplurality of scanning lines into an on state and to turn the thin filmtransistor that is connected to the plurality of scanning lines into anon state.